The upsides:
Before getting into a discussion of the detrimental effects of vibration on the human body, it is worth asking if there are any upsides.
It would appear that there are. It is claimed that low-amplitude, low-frequency mechanical stimulation of the human body is a safe and active method to improve muscle strength, bone remodelling, and cartilage preservation, particularly in patients with related disorders such as osteoporosis and osteoarthritis. However, the mechanisms mediating these effects are not well known. These techniques are also being used to enhance athletic performance. It should be noted that most sites promoting this type of therapy also state that it is not yet clear if it’s as good for you as regular exercise.
For this type of whole-body vibration, you stand, sit, or lie on a machine with a vibrating platform. The activity may cause you to feel as if you’re exerting yourself. Advocates say that as little as 15 minutes a day, three times a week of this activity may aid weight loss, burn fat, improve flexibility, enhance blood flow, reduce muscle soreness after exercise, build strength, and decrease the stress hormone cortisol.
The downsides:
The detrimental effects of vibration on the human body are both more extensive and better understood than the upsides.
The negative effects of prolonged vibration are generally categorised into:
- Musculoskeletal systems – chronic back and neck pain, degeneration of spinal discs, and muscle weakening. Caused by prolonged use of things like handheld power tools such as jackhammers and chainsaws.
- Whole-body vibration risks – potential for motion sickness, headaches, digestive issues, and cardiovascular strain. Caused by prolonged exposure to off-road vehicles, trucks, jet boats, and even by heavy machinery via floors.
- Neurological effects – reduced motor skills, loss of balance, and cognitive decline, including fatigue and decreased attention. Examples are permanent numbness in fingers and “white finger”, both typically caused by prolonged use of handheld power tools.
The severity of the impact will vary with:
- Intensity and
- Frequency of the vibration
- Duration.
And increased risk occurs with:
- Cold environments
- Poor posture – e.g. working in awkward positions
- Individual factors – e.g. age, pre-existing conditions.
So what vibration frequencies are harmful to humans?
As a broad statement, frequencies less than 20 Hz and more than 70 Hz are considered most dangerous to the human body. Most damage is induced when the vibration frequency matches the resonant frequency of the body or a body part. This match will lead to excessive vibrations and malfunctions.
Very briefly, the resonant frequency is the natural rate at which an object or system vibrates with maximum amplitude when exposed to an external force. For example, the resonant frequency of the human body is generally considered to be in the range of 3 – 10 Hz, but individual organs have different resonant frequencies – e.g:
- Skull/brain is 13.9 – 14.3 Hz but the whole head is about 23 Hz
- Lungs are 25 Hz for men and 33 Hz for women
- Eyes have a range of 30 – 80 Hz.
The most common standard used in Australia for measuring the impact of vibration on the human body is BS 6472:1992 and there is the NSW EPA “Assessing Vibration: a technical guideline” of 2006.
Vibration Dose Value (VDV) is the recommended parameter to measure. VDV is a cumulative, fourth-power, frequency-weighted measurement. The fourth-power method ensures a heavy weighting of short-term, jarring shocks. Importantly, VDV measurements are not instantaneous measurements. A minimum of 2 hrs is recommended, but, if possible, measurements across a full working day are preferable.
The Texcel VDV sensor uses low range triaxial accelerometers which have been band limited from 0.4 Hz to 100 Hz as required by the above standards.
If you would like to discuss these issues further, please give us a call.